Diffusion and Protecting Barrier Layers in a Substrate Supported SOFC Concept

Kurzfassung

High temperature fuel cells of SOFC type as direct converter of chemical into electrical en-ergy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced light-weight planar cells for electricity supply systems in cars and other mobile systems. Such cells, in one current de-sign, consist mainly of metallic parts, e.g. of ferrite steels. These cells shall operate in the temperature range of 700 to 800°C where oxidation and diffusion processes can be of det-rimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of volatile Cr-species from interconnects into the triple phase boundary (TPB) on the cathode side forming electrochemical reaction inhibiting phases. Furthermore, on the anode side a mutual diffusion of ferritic substrate and anode material, e.g. iron and chro-mium from the ferrite into the anode and nickel from the anode into the ferrite can occur resulting in undesirable phase and structure transformations. Both cases of degradation mechanisms significantly reduce performance and system lifetime. A possible solution of these problems is seen in protecting intermediate layers, which can reduce such effects considerably if they are dense, stable and of high electronic conductivity. Perovskite-type layers (e.g. doped LaCrO3) applied with high-velocity Direct Current-Vacuum Plasma Spraying (DC-VPS) promise to solve reliably such problems.